Chlorophyll fluorescence effects on vegetation apparent reflectance: II. Laboratory and airborne canopy-level measurements with hyperspectral data

Relationships found between Compact Airborne Spectrographic Imager (CASI) h yperspectral canopy reflectance measurements at laboratory and field levels with PAM-2000 chlorophyll fluorescence data are presented. This is a conti nuation of the paper where relationships at the leaf level between leaf ref lectance and chlorophyll fluorescence were found and demonstrated to the co nsistent with theory using the Fluorescence-Reflectance-Transmittance (FRT) model. Experiments using the hyperspectral CASI sensor in the laboratory t o observe a canopy of maple seedlings are performed as an intermediate step to demonstrate the link between the results at leaf-level and the CASI fie ld canopy levels. Scene observations of the seedling utilizing a long-pass blocking filter showed that apparent canopy reflectance in the laboratory i s affected by changes in fluorescence emissions. A laboratory experiment on seedlings on seedlings subjected to diurnally induced change shows the str ong link between CASI canopy reflectance optical indices in the 680-690-nm region and Fv/Vm dark-adapted chlorophyll fluorescence. Stressed and health y maple seedlings are used to demonstrate the use of optical indices calcul ated from the 680-690-nm spectral region to track changes in steady-state f luorescence: the curvature index R6832/(R675-691) and the R685/R655 ratio c alculated from the canopy reflectance are related to leaf-measured Ft, Fm' and DeltaF/Fm' steady-state features, and are in agreement with theoretical simulations using the leaf Fluorescence-Reflectance-Transmittance model. T o test these findings in a field setting, airborne field hyperspectral CASI data of 2-m spatial resolution, 7.5-nm spectral resolution, and 72 channel s was used, collected in deployments over 12 sites of Acer saccharum M. in the Algoma Region, Ontario (Canada) in 1997 and 1998. A field sampling camp aign was carried out for biochemical contents of leaf chlorophyll and carot enoids, chlorophyll fluorescence, and leaf reflectance and transmittance. L eaf-level relationships obtained between optical indices and physiological indicators were scaled up to canopy level through canopy reflectance models using input model parameters related to the canopy structure and viewing g eometry at the time of data acquisition. Results show that scaled-up optica l indices in the 680-690-nm region are related to Fv/Fm chlorophyll fluores cence measured in the 20x20-m study sites. Consistency between leaf, labora tory, and field canopy hyperspectral data is shown in this and the previous paper, demonstrating the effect of fluorescence on observations of apparen t vegetation reflectance. (C) Elsevier Science Inc., 2000.